Pharmacokinetic Interaction Between Nitazoxanide and Atazanavir/Ritonavir in Healthy Volunteers

Nitazoxanide is an antiprotozoal drug with a well-understood and documented safety profile. It was first approved by the US Food and Drug Administration (FDA) in July 2004 for the treatment of diarrhoea caused by Giardia lamblia or Cryptosporidium parvum in adults (≥ 18 years) and paediatrics (1-17 years). Nitazoxanide has also demonstrated in-vitro anti-SARS-CoV-2 activity. A review of in vitro studies reporting the anti-coronavirus activity of nitazoxanide and its active metabolite, tizoxanide, is available. Nitazoxanide was among the three top inhibitors of coronavirus replication, resulting in a reduction of 6 log10 in virus titer with an IC50 of 1.0 µM. The major circulating metabolite of nitazoxanide is tizoxanide, and it has also been confirmed to have activity against SARS-CoV-216. Both suppress the cytopathic effect of SARS-CoV-2. Nitazoxanide is also active against the influenza A virus and was shown to reduce symptom duration in uncomplicated acute influenza. Since SARS-CoV-2 shares almost 80% of the genome with SARSCoV19 and almost all encoded proteins of SARS-CoV-2 are homologous to SARS-CoV proteins, nitazoxanide and its metabolite tizoxanide with demonstrated activity against SARS-CoV are likely to be effective against SARS-CoV-2. Since the virus replicates quickly, antivirals must remain active across their dosing interval. Therefore, enhanced drug concentration will be needed in the lung throughout the dosing interval.

The HIV protease inhibitor, atazanavir (boosted with ritonavir), has been shown to inhibit the major protease enzyme required for viral polyprotein processing during coronavirus replication. It also blocks pro-inflammatory cytokine production. Similar to nitazoxanide, atazanavir has been shown to achieve effective concentration in the pulmonary tissues at the approved dose of 300 mg in combination with 100 mg of ritonavir, with even more favourable ratios when compared to in vitro activities generated in human cell models.

Therefore, based on these considerations, the combination of nitazoxanide (taken orally at 1000 mg twice daily) and atazanavir/ritonavir (taken orally at 300/100 mg once daily) is being considered for selection for intervention for the treatment of COVID-19. Hence, this study wants to evaluate the clinical usefulness of the combination of these drugs. The approach is to characterise the extent of drug-drug interaction of nitazoxanide and atazanavir/ritonavir when 1000 mg nitazoxanide is taken two times daily in combination with 300/100 mg atazanavir/ritonavir before deploying the combination for the intervention.